[SERVER_PORT] when using proxy-server

I'm using Litespeed SE(as backend for scripts, on port 8080), nginx(as frontend proxy-server, on port 80) and PHP LSAPI, where each site(domain) has own vhost, php.ini, listener with own port(8081, 8082...)
And the problem is that some php-scripts(like phpBB3, phpMyAdmin) are using port(requesting it by _SERVER['SERVER_PORT']) in the redirection URL if it's not 80 by default - so URL redirects like http://mysite.com:8081/blah.php?=blah...... lead to an error.
So is there any way to return port 80(in _SERVER['SERVER_PORT']) dy default for all vhosts instead of port mentioned in the listener for this vhost(i.e. 8081, 8082, 8083...)? And does this have to be done on Litespeed, nginx or PHP level?
I will be glad to listen to any helpful solution.

Thanks in advance!

P.S. If it'll be useful, here's example nginx config, that I'm using for each vhost:

a few things to note:
1. LSWS Stand Edition only reads up to 5 vhosts from Apache httpd.conf. If you have more vhosts than that, you will be unable to server others vhosts.
2. make sure LSWS listener is on 127.0.0.1:8081 (or any IP:8081).
3. _SERVER['SERVER_PORT'] is PHP environment variable. in your case, it will reflect the port backend server LSWS listens on (i.e., 8081).